Type 1 diabetes (T1D) develops when insulin-secreting b-cells, found in the pancreatic islets of Langerhans, are destroyed by infiltrating T cells. How human T cells recognize b-cell-derived antigens remains unclear. Genetic studies have shown that HLA and insulin alleles are the most strongly associated with risk of T1D. These longstanding observations implicate CD4 + T-cell responses against (pro)insulin in the pathogenesis of T1D. To dissect the autoimmune T-cell response against human b-cells, we isolated and characterized 53 CD4 + T-cell clones from within the residual pancreatic islets of a deceased organ donor who had T1D. These 53 clones expressed 47 unique clonotypes, 8 of which encoded proinsulin-specific T-cell receptors. On an individual clone basis, 14 of 53 CD4 + T-cell clones (26%) recognized 6 distinct but overlapping epitopes in the C-peptide of proinsulin. These clones recognized C-peptide epitopes presented by HLA-DQ8 and, notably, HLA-DQ8 transdimers that form in HLA-DQ2/-DQ8 heterozygous individuals. Responses to these epitopes were detected in the peripheral blood mononuclear cells of some people with recent-onset T1D but not in HLAmatched control subjects. Hence, proinsulin-specific, HLA-DQ8, and HLA-DQ8-transdimer-restricted CD4 + T cells are strongly implicated in the autoimmune pathogenesis of human T1D.Type 1 diabetes (T1D) is an autoimmune disease caused by the CD4 + and CD8 + T-cell-mediated destruction of pancreatic insulin-producing b-cells (1). b-Cell destruction leads to primary insulin deficiency, which is treated by exogenous insulin therapy, and currently there is no cure. The pathogenesis of T1D has been well characterized using the NOD mouse model, but the immune basis of T1D in humans is less clear.Genetic association studies have provided powerful insights into the etiology of human T1D (2,3). The HLA class II region has the strongest impact on risk of T1D. Some HLA alleles-DQB1*06:02 for example-dominantly protect against T1D (4). In contrast, of all alleles, HLA-DQ2

Type 1 diabetes (T1D) is an autoimmune disease in which insulin-producing beta cells, found within the islets of Langerhans in the pancreas, are destroyed by islet-infiltrating T cells. Identifying the antigenic targets of beta-cell reactive T cells is critical to gain insight into the pathogenesis of T1D and develop antigen-specific immunotherapies. Several lines of evidence indicate that insulin is an important target of T cells in T1D. Because many human islet-infiltrating CD4+ T cells recognize C-peptide–derived epitopes, we hypothesized that full-length C-peptide (PI33–63), the peptide excised from proinsulin as it is converted to insulin, is a target of CD4+ T cells in people with T1D. CD4+ T cell responses to full-length C-peptide were detected in the blood of: 14 of 23 (>60%) people with recent-onset T1D, 2 of 15 (>13%) people with long-standing T1D, and 1 of 13 (<8%) HLA-matched people without T1D. C-peptide–specific CD4+ T cell clones, isolated from six people with T1D, recognized epitopes from the entire 31 amino acids of C-peptide. Eighty-six percent (19 of 22) of the C-peptide–specific clones were restricted by HLA-DQ8, HLA-DQ2, HLA-DQ8trans, or HLA-DQ2trans, HLA alleles strongly associated with risk of T1D. We also found that full-length C-peptide was a much more potent agonist of some CD4+ T cell clones than an 18mer peptide encompassing the cognate epitope. Collectively, our findings indicate that proinsulin C-peptide is a key target of autoreactive CD4+ T cells in T1D. Hence, full-length C-peptide is a promising candidate for antigen-specific immunotherapy in T1D.

Previous attempts of α-1,3-galactocyltransferase knockout (GalTKO) pig bone marrow (BM) transplantation (Tx) into baboons have demonstrated a loss of macro-chimerism within 24 h in most cases. In order to achieve improved engraftment with persistence of peripheral chimerism, we have developed a new strategy of intra-bone BM (IBBM) Tx. Six baboons received GalTKO BM cells, with one-half of the cells transplanted into the bilateral tibiae directly and the remaining cells injected intravenously (IBBM/BM-Tx) with a conditioning immunosuppressive regimen. In order to assess immune responses induced by the combined IBBM/BM-Tx, three recipients received donor SLA-matched GalTKO kidneys in the peri-operative period of IBBM/BM-Tx (Group 1), and the others received kidneys 2 months after IBBM/BM-Tx (Group 2). Peripheral macro-chimerism was continuously detectable for up to 13 days (mean 7.7 days; range 3–13) post-IBBM/BM-Tx and in three animals, macro-chimerism reappeared at days 10, 14 and 21. Pig CFUs, indicating porcine progenitor cell engraftment, were detected in the host BM in four of six recipients on days 14, 15, 19 and 28. In addition, anti-pig unresponsiveness was observed by in vitro assays. GalTKO/pCMV-kidneys survived for extended periods (47 and 60 days). This strategy may provide a potent adjunct for inducing xenogeneic tolerance through BM-Tx.

SummaryType 1 diabetes (T1D) develops when there are insufficient insulinproducing beta cells to maintain glucose homeostasis. The prevailing view has been that T1D is caused by immune-mediated destruction of the pancreatic beta cells. However, several recent papers have challenged the long-standing paradigm describing T1D as a tissue-specific autoimmune disease. These authors have highlighted the gaps in our knowledge and understanding of the aetiology of T1D in humans. Here we review the evidence and argue the case for the autoimmune basis of human T1D. In particular, recent analysis of human islet-infiltrating T cells brings important new evidence to this question. Further data in support of the autoimmune basis of T1D from many fields, including genetics, experimental therapies and immunology, is discussed. Finally, we highlight some of the persistent questions relating to the pathogenesis of human type 1 diabetes that remain to be answered.